This is not Young Adult. It's very adult, and I liked it very much. It's complex in all the ways I like complexity, without using ideas as a shield around characters I don't care about. Characters, plot, and ideas all work together really well, and that's a rare thing.
There's a lot of detail here about oppression and othering. Should I go into world history first? That seems right. For a very long time in this fiction, the Continent was the preeminent power in the world, particularly since it had very real and present gods that looked after their affairs. Saypur had no gods, and its people were looked on as less than human and ruthlessly oppressed.
My chronology might be a bit off, but about 60 years ago, Saypur rose under a general, the Kaj, who discovered how to kill gods, and did so. That caused all sorts of cataclysms on the Continent that I will not detail - but they are amazingly vivid to discover when you come across them in the book. Now Saypur is dominant, and for the most part, seems to be setting out to be just as repressive as their forrmer oppressors. Those on the Continent are barred from even knowing about their history, speaking of or honouring their lost gods, or in any way having a past.
The Continentals are not chastened. In fact, some of them persist in seeing the Saypuri as less-than-human. There aren't easy sides to take here, no clear benevolent force in the midst of displays of power. Hate flows from both sides, justified and unjustified.
Into this, a murder mystery. The murder mystery and the strange city meant that this book reminded me quite a lot of The City and the City by China Mieville, at least initially. An eminent historian from Saypur there to study the Continent is found dead. A Saypur spy shows up to investigate, and she knows far more about the Gods than most would.
(Also she's accompanied by a giant Sigrud, whom I totally loved. Shara and Sigrud both.)
She's undermined by her superiors back home, hated by the Continentals around her, regarded with suspicions by the Saypuri dignitaries in Bulikov, the City of Stairs. It's a classic story of fighting alone (or almost alone) against all comers.
There is also an ex-lover and a sideplot about sexuality under the Continent and on Saypur, and how it is tied up with certain Gods, particularly the one who was all about law and order.
Of course, as the story goes on, it becomes apparent that the Divine might not be as dead as the Saypuri thought, and that might not be as good a thing for the Continentals waiting for a return of their glorious past as they thought.
There are some really great twists in this book, the kind that you don't even know will be coming, but which reframe things in profound and sometimes shocking ways. Bennett has done a really masterful job of layering in ideas and then bringing them to fruition in startling ways.
Overall, this book is really excellent, and I can't wait to read the next. It was a pleasant surprise, not just that it was more adult than I was expecting, but then also that it was so damned good.